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MDEV-21921 Make transaction_isolation and transaction_read_only into system variables

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In MariaDB, we have a confusing problem where:
* The transaction_isolation option can be set in a configuration file, but it cannot be set dynamically.
* The tx_isolation system variable can be set dynamically, but it cannot be set in a configuration file.

Therefore, we have two different names for the same thing in different contexts. This is needlessly confusing, and it complicates the documentation. The same thing applys for transaction_read_only.

MySQL 5.7 solved this problem by making them into system variables. https://dev.mysql.com/doc/relnotes/mysql/5.7/en/news-5-7-20.html

This commit takes a similar approach by adding new system variables and marking the original ones as deprecated. This commit also resolves some legacy problems related to SET STATEMENT and transaction_isolation.
This commit is contained in:
Junqi Xie
2023-03-12 13:55:30 +08:00
committed by Daniel Black
parent 4472a7b4ff
commit d20a96f9c1
100 changed files with 1232 additions and 962 deletions
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12
sql/sql_class.h
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@ -3505,15 +3505,15 @@ public:
/*
Current or next transaction isolation level.
When a connection is established, the value is taken from
@@session.tx_isolation (default transaction isolation for
the session), which is in turn taken from @@global.tx_isolation
(the global value).
@@session.transaction_isolation (default transaction isolation
for the session), which is in turn taken from
@@global.transaction_isolation (the global value).
If there is no transaction started, this variable
holds the value of the next transaction's isolation level.
When a transaction starts, the value stored in this variable
becomes "actual".
At transaction commit or rollback, we assign this variable
again from @@session.tx_isolation.
again from @@session.transaction_isolation.
The only statement that can otherwise change the value
of this variable is SET TRANSACTION ISOLATION LEVEL.
Its purpose is to effect the isolation level of the next
@ -3523,13 +3523,13 @@ public:
transaction, this assignment (naturally) only affects the
upcoming transaction.
At the end of the current active transaction the value is
be reset again from @@session.tx_isolation, as described
be reset again from @@session.transaction_isolation, as described
above.
*/
enum_tx_isolation tx_isolation;
/*
Current or next transaction access mode.
See comment above regarding tx_isolation.
See comment above regarding transaction_isolation.
*/
bool tx_read_only;
enum_check_fields count_cuted_fields;